Fertilizer is made from a phosphoric acid liquor which incidentally contains significant amounts of uranium, typically about 0.2 g/l. In order not to waste the valuable uranium, processes have been developed by Oak Ridge National Laboratories to separate it from the acidic liquor which is contaminated with metal ions, principally iron in a typical amount of about 12 g/l or more.
The Oak Ridge "DAPEX" process is a cationic process divided into two extraction cycles. (See the article in I&EC Process Design and Development, Vol. II, page 122, January 1972 by F. J. Hurst, D. J. Crouse, and K. B. Brown titled "Recovery of Uranium from Wet-Process Phosphoric Acid." The same process is described in more detail by F. J. Hurst et al. in ORNL-TM-2522 Report titled "Solvent Extraction of Uranium From Wet-Process Phosphoric Acid," April 1969. Also see U.S. AEC Report, ORNL 2952, June 30, 1960 by F. J. Hurst and D. J. Crouse, titled "Recovery of Uranium from D2EHPA Extractant with (NH.sub.4).sub.2 CO.sub.3.") In the first cycle the uranyl ion (UO.sub.2.sup..sup.+2) and some ferric ion are extracted using di-2-ethylhexyl phosphoric acid (D2EHPA) in kerosene, the uranyl ion forming a complex with the D2EHPA. The solvent is then stripped with a portion of the acid leaving the extractor and containing ferrous ion to produce a concentrated acidic aqueous stream of ferrous and uranous (U+4) ions. The uranous ion is then oxidized with air to the uranyl ion.
In the second cycle of the DAPEX process the concentrated acidic, aqueous stream from the first cycle is again extracted with kerosene containing D2EHPA, then stripped with water containing 2 to 2.5 moles/l (NH.sub.4).sub.2 CO.sub.3 which precipitates ammonium-uranyl-tricarbonate (AUT), (NH.sub.4).sub.4 UO.sub.2 (CO.sub.3).sub.3, and some ferric hydrate. The AUT could then be recrystallized to purify it.
The DAPEX process typically recovered about 94% of the uranium in the feed and produced uranium containing 2 to 4% iron (based on the uranium) before recrystallizaton. Ceramic grade uranium, which is used as fuel in reactors, requires no more than 0.04% iron (based on the uranium). (All percentages herein are by weight unless otherwise indicated.)
Oak Ridge National Laboratories has also developed an anionic exchange uranium extraction process called the "AMEX" process. (See the article by D. J. Crouse and K. B. Brown titled "Amine Extraction Processes for Uranium Recovery from Sulphate Liquors, Vol. I," U.S. Atomic Energy Commission, ORNL-1959, Sept. 30, 1955 and the article by D. J. Crouse et al. titled "Progress Report on Separation and Recovery of Uranium and Thorium from Sulfate Liquor by the AMEX Process," U.S. Atomic Energy Commission, ORNL-2173, Jan. 1, 1957). The AMEX process, because of the anionic exchange mechanism of the amines, is generally used to extract uranium from sulfuric acid leach liquors containing 1.0 to 2.0 g/l of uranium. The sulfuric acid liquor is contacted with an organic solvent containing long chain alkylamines. The uranium can be stripped from the organic solvent using ammonium carbonate. The AMEX process is reported to extract at least 95% of the uranium with about 2% contaminants, based on the uranium.